It is essential that the space between the glass sheets of an insulating-glass panel of the type described above be perfectly sealed with respect to the exterior, so that dirt cannot enter this space and so that condensation cannot occur therein. This is typically done by first forming a sandwich of two perfectly clean and identical glass sheets flanking an annular spacer ring that lies somewhat inward of the aligned outer peripheries of these sheets, a procedure carried out in a controlled environment of low-humidity clean air. Then the outwardly open groove that runs around the edge of this sandwich between the sheets is filled with a viscous synthetic-resin mass that hardens, adhering to both sheets and to the spacer. Once hard this mass totally seals off the space between the sheets.
In a production-line operation this sealing of the edges is done by an automatic extruding device such as described in German patent documents 2,834,902 and 2,845,475 (see also U.S. Pat. Nos. 3,974,011 and 3,947,311. This device is a pendant head which is suspended above a conveyor that can move the workpieces past underneath it. The extruder head can rotate about a vertical axis. The conveyor is provided underneath this head, which is normally set up so it can move longitudinally in the travel direction and transversely thereto, with a short transverse conveyor, with clamping devices, and with some stops.
This apparatus carries out the following eight-step procedure to seal the edge of an assembled sandwich of two sheets and a peripheral spacer:
(A) The sandwich is fed longitudinally in the normal transport direction to the sealing location underneath the sealing device and the leading edge is positioned.
(B) The sandwich is then shifted transversely against a transverse stop so that its longitudinal edges are positioned transversely.
(C) The transverse stop is moved away from the sandwich which is clamped in place in the station.
(D) The sealing device is moved into position at the edge of the sandwich.
(E) The nozzle and position sensor of the sealing device are tilted to engage into the groove at the edge of the sandwich.
(F) The sealing device then travels transversely and longitudinally around the workpiece, changing direction at each corner, to seal all its edges.
(G) The nozzle is withdrawn from the workpiece.
(H) The sealed sandwich is released and moved longitudinally out of the sealing station.
Steps (D) through (G) utilize the mobile sealing device, but during steps (A) through (C) and (H), the so-called dead time of the system, this device is not used. This style of production therefore leaves a valuable piece of equipment idle for often about half the time. Such nonuse is not only inefficient in itself, but is particularly bad for a device that is extruding a hot synthetic resin, as during the dead time the resin can harden or cure in the nozzle.